Drum type switch



y 14, 1963 c. COBBETT 3,089,938

DRUM TYPE SWITCH Filed March 1, 1960 26 FIG.3

IN V EN TOR. Leonard C. Cobbeff ilnited States This invention relates to a drum type switch particularly adapted for use as a low voltage, high current switch.

The invention has for an object to provide a novel and improved drum type switch of the character specified which is characterized by fixed contacts having novel flexure mountings and which are capable of maintaining a uniform contact pressure against the drum to enable them to carry a relatively high current without overheating.

The invention has for another object to provide a novel and improved low voltage, high current switch of the character specified having fixed contact mountings of novel structure particularly adapted to dissipate heat losses generated within the switch.

A further object of the invention is to provide a novel and improved switch of the character specified having fixed contacts provided with flexure mountings which are capable of maintaining uniform contact pressures whereby to clean the contact surfaces of contaminants and to penetrate the surface film at a suflicient number of contact points to carry the rated current.

A still further object of the invention is to provide a novel and improved switch of the character specified wherein the current is interrupted at places other than the normal areas whereby to protect such normal contact current areas from roughening and scoring due to the rupturing of heavy currents.

With these general objects in view and such others as may hereinafter appear, the invention consists in the drum type switch particularly adapted for switching of high currents at low voltage as hereinafter described and particularly defined in the claims at the end of this specification.

In the drawings illustrating the preferred embodiment of the invention:

FIG. 1 is a perspective view of the present drum type switch embodying the novel flexure mountings for the fixed contacts;

FIG. 2 is a plan view of the switch; and

FIG. 3 is a side elevation of the same.

In general the present invention contemplates a drum type switch particularly adapted for use in a circuit having high currents at low voltage and includes spaced, stationary silver-faced contact members, each having a semirigid fiexure mounting of novel structure adapted to apply relatively high pressure against a segmental silverfaced drum surface which is rotatable into and out of bridging engagement with the spaced contacts to close and open the circuit. The flexure mounting for each contact member includes a plurality of spaced parallel flexure members anchored at their extremeties to the contact member and a base member. The contact member thus mounted provides a semirigid structure adapted to apply substantially uniform pressure when engaged by the segmental surface of the cylindrical drum and to resiliently maintain the contacts in high pressure engagement with the drum surface.

Referring now to the drawings, the illustrated low voltage high current switch includes a manually rotatable cylindrical drum having a silver-faced segmental surface 12 arranged to be rotated to bridge spaced contact members 14 having silver-faced engaging surfaces 15. The cylindrical drum 10 may be fixed to the lower end of a vertical shaft 16 by set screws 18. The shaft 16 is supatent U" 3,089,938 Patented May 14, 1963 ice ported for rotation in upper and lower angle brackets 20, 22, respectively, which extend from and are secured to the front face of an insulating panel 24- by bolts 26.

As herein shown, each contact member 14 is mounted on the outer ends of a plurality of spaced parallel flexure members 28 comprising flat elongated and relatively stiff conductive metal plates, such as hard rolled copper plates, capable of flexing. The inner ends of the flexure plates are secured in a conductive metal base terminal member 30 bolted to the insulating panel 24. The inner ends of the fiexure members 28 are fitted into spaced vertical grooves 29 formed in the terminal member 30, and the outer ends of the fiexure members are fitted into spaced vertical grooves 31 formed in the contact member 14. The ends of the flexure members 28 may be secured in the grooves by a tight press fit, or may be soldered, welded or otherwise secured to provide an integral connection between the base terminal member 30 and the contact member 14. The base terminal members 30 may be provided with appropriate means, not shown, extending through the insulating panel for electrical connection in a circuit. The upper end of the vertical shaft 16 may be provided with an opening 32 for receiving an operating handle 34 or motor drive coupling by which the drum 10 may be rotated.

The flat elongated fiexure members 28 are arranged in a plane parallel to the vertical axis of the drum 10 to provide a relatively stiff, semirigid, spring loaded structure arranged to resiliently urge the contacts 14 in a horizontal plane into high presure engagement with the segmental surface 12 of the drum 10 when the latter is rotated into bridging engagement with the spaced contact members. As shown in FIG. 2, the opposed contact members 14 are aligned with the diametral central line of the drum 10, and the arc defined by the segmental surface 12 of the drum extends beyond preferably about 200 as illustrated. The silver-faced engaging surface of opposed contact members are preferably flat so that the contact area comprises a line contact at the points of tangency with the arcuate silver-faced engaging surfaces of the drum.

The terminal base members 30 and the silver-faced contacts 14 preferably comprise a high conductivity metal, such as hard copper, and the silver-faced drum may also comprise a hard copper material. As herein illustrated, each contact assembly comprises three vertically spaced individual fingerlike contact units 14 whereby to assure high pressure resilient engagement of the different units with the length of the bridging drum 10 through parallel paths, the flexure members 28 of each unit being connected with the base terminal member 30. This expedient permits independent movement of each fingerlike unit to effect self-alignment and independent seating of each unit with the elongated surfaces of the bridging drum whereby to compensate for any irregularities in such surfaces and to assure substantially uniform pressures against the length of the bridging surfaces.

From the description thus far it will be seen that in operation when the drum 10' is rotated into bridging engagement with opposed contact assemblies '14 the relatively stiff flexing structure will maintain relatively high unit pressures against the segmental surfaces 12 of the drum, sufficient to clean the engaging surfaces of contaminants and to penetrate the surface film at an ade quate number of contact points to carry the rated current without overheating. The relatively stiff flexing structure is preferably designed to apply a predetermined contact pressure, sufiicient to maintain an efficient contact without undue or excess pressure so as to avoid undue scoring between the silver-faced surfaces. In practice such contact pressure may range from 1500 to 3000 pounds per square inch for displacement and the drum surface may be lubricated with a fatty oil. In practice the contact members 14 are provided with a fine silver facing 15, and the segmental drum surface is provided with a coin silver facing, this expedient being found to reduce scoring of the engaging surfaces to a minimum. These facings extend beyond and around the edges of member 14 and edges of the segmental surface of drum 10, thereby providing an entering radius for engaging the leading edges of surfaces 12, 15 as the drum is rotated.

The unit pressures per unit of displacement of the flexing contact structure may be varied for different designs and sizes of switches embodying the present invention by changing the length of the flexure members, longer flexure members providing more flexibility and less pressure and, conversely, shorter flexure members providing a stiffer and less resilient structure and, consequently, more pressure. The number of flexure members, and also the cross sectional dimensions and spacing of the flexure members may also be varied to provide the preferred pressure. In the illustrated embodiment of the invention, for example, the hard rolled copper flexure members may be about one-sixteenth gauge, and the spacing between the members may be about one-sixteenth to three thirty-seconds. The length of the fiexure members in the illustrated embodiment of the invention may be about three inches.

It will be observed that in operation the flat engaging surface 15 is resiliently urged into tangential contact with and follows the contour of the segmental surface 12 of the drum. The line of tangency thus formed moves from the diametral center line to the rounded trailing edges of surfaces 12, 15 when the drum is rotated to disengage the switch. Thus, the circuit is interrupted at places spaced from the normal current carrying areas so that any erosion of the contact material caused upon interruption of the current will occur at places other than the normal contact carrying areas. The current carrying areas are thus protected from roughening and scoring due to the rupturing of heavy currents to thus prolong the life of the switch.

Another important feature of the present invention resides in the spaced structure of the fiexure members 28 which permits free or forced flow of air therebetween to rapidly dissipate heat losses and increase the capacity of the switch. It will also be observed that the flexure members 28 provide a stiff, semirigid spring loaded motion in a horizontal direction while presenting a rigid structure in all other planes of motion.

From the above description it will be seen that the present current interrupting drum type switch is particularly adapted for use in the switching of high currents at low voltage in a novel and efiicient manner.

While the preferred embodiment of the invention has been herein illustrated and described, it will be understood that the invention may be embodied in other forms within the scope of the following claims.

Having thus described the invention, what is claimed 1. A drum type switch particularly adapted for use as a low voltage high current switch comprising an insulating panel, a rotatable drum having a segmental arcuate conducting surface extending through an arc of substantially more than and having marginal edges raised above the remaining non-conducting surface of the drum, a pair of diametrically opposed contact members having flat engaging surfaces cooperating with the conducting surface of the drum providing a line contact at the points of taugency when the drum is rotated into normal full contacting engagement with the flat contact members, each of said contact members having a base terminal secured to said insulating panel, and a flexible mounting connecting the contact member and its base terminal providing a semi-rigid resilient contact structure adapted to apply uniform pressure against the conducting surface of the drum, the edges of said arcuate conducting surface engaging the adjacent edges of said fiat resilient contacts upon make and break of the contacts at points of tangency spaced from the points of tangency engaged when the switch is in full contacting engagement whereby the areas of the contacting elements which are subject to pitting and erosion upon make and break of the contacts are different from the normally closed contact areas.

2. A drum type switch as defined in claim 1 wherein each flexible mounting comprises a plurality of relatively closely spaced, parallel and relatively stiff leaf springs of conductive metal independently secured at their ends to said contact members and said base terminals, the spacing between adjacent leaf springs permitting a free flow of air therebetween for dissipation of heat generated within said switch.

3. A drum type switch as defined in claim 2 wherein each flexibly mounted contact comprises an assembly of a plurality of separate longitudinally spaced individual flexible units, each unit being capable of independent lateral flexing movement to present its fiat contacting surface against longitudinally spaced points of the conducting surface of the drum whereby to provide high pressure resilient contact along spaced points of the drum through parallel paths, each separate unit being capable of independent flexing movement to permit self-alignment and independent seating of each spaced unit with the contacting surface of the drum whereby to compensate for any irregularities in the conducting surface and to assure substantially uniform pressures against said conducting surface.

References Cited in the file of this patent UNITED STATES PATENTS 301,023 Weston June 24, 1884 1,065,567 Wagner June 24, 1913 1,146,204 Pearce July 13, 1915 1,890,822 Murray Dec. 13, 1932 1,893,046 Austin Jan. 3, 1933 

1. A DRUM TYPE SWITCH PARTICULARLY ADAPTED FOR USE AS A LOW VOLTAGE HIGH CURRENT SWITCH COMPRISING AN INSULATING PANEL, A ROTATABLE DRUM HAVING A SEGMENTAL ARCUATE CONDUCTING SURFACE EXTENDING THROUGH AN ARC OF SUBSTANTIALLY MORE THAN 180* AND HAVING MARGINAL EDGES RAISED ABOVE THE REMAINING NON-CONDUCTING SURFACE OF THE DRUM, A PAIR OF DIAMETRICALLY OPPOSED CONTACT MEMBERS HAVING FLAT ENGAGING SURFACES COOPERATING WITH THE CONDUCTING SURFACE OF THE DRUM PROVIDING LINE CONTACT AT THE POINTS OF TANGENCY WHEN THE DRUM IS ROTATED INTO NORMAL FULL CONTACTING ENGAGEMENT WITH THE FLAT CONTACT MEMBERS, EACH OF SAID CONTACT MEMBERS HAVING A BASE TERMINAL SECURED TO SAID INSULATING PANEL, AND A FLEXIBLE MOUNTING CONNECTING THE CONTACT MEMBER AND ITS BASE TERMINAL PROVIDING A SEMI-RIGID RESILIENT CONTACT STRUCTURE ADAPTED TO APPLY UNIFORM PRESSURE AGAINST THE CONDUCTING SUFACE OF THE DRUM, THE EDGES OF SAID ARCUATE CONDUCTING SURFACE ENGAGING THE ADJACENT EDGES OF SAID FLAT RESILIENT CONTACTS UPON MAKE AND BREAK OF THE CONTACTS AT POINTS OF TANGENCY SPACED FROM THE POINTS OF TANGENCY ENGAGED WHEN THE SWITCH IS IN FULL CONTACTING ENGAGEMENT WHEREBY THE AREAS OF THE CONTACTING ELEMENTS WHICH ARE SUBJECT TO PITTING AND EROSION UPON MAKE AND BREAK OF THE CONTACTS ARE DIFFERENT FROM THE NORMALLY CLOSED CONTACT AREAS. 